The present invention relates to an exhaust gas recirculation valve device disposed in an exhaust gas recirculation passage of an internal combustion engine for example of an automobile.
FIG. 1 is a cross sectional figure showing the internal structure of a conventional exhaust gas recirculation valve device. In the figure, the valve housing 1 has an inlet port 2 communicating with an exhaust system (not shown) of an engine which is an internal combustion engine, an outlet port 3 which communicates with an air intake system (not shown) of the engine and a passage 4 interposed between the outlet port 3 and the inlet port 2. A valve seat 5 is press fitted into the passage 4. 6 is a valve rod passing through a bushing 7. A valve 8 is mounted on the lower end of the valve rod 6 to separate or abut with the valve seat 5. 9 is a holder to prevent deposition of substances in the bushing 7. 10 is a spring holder which is pushed upwardly by a coil spring 11. A through hole 12 is formed in the central section of the spring holder 11. The tip 6a of the valve rod 6 is fixed by caulking through the through hole 12. The valve rod 6 and the spring holder 10 are integrated by caulking and the valve 8 mounted on the lower section of the valve rod 6 is normally pushed in a closed position with respect to the valve seat 5 by the coil spring 11. 13 is a cooling water passage cooling the motor to be described below and the valve body.
20 is a stepping motor main body functioning as a stator assembly with respect to the rotor section to be discussed below. A motor holder 21 is fixed to the lower section of the stepping motor 20 by a clamp screw 23 through an O-ring 22 in order to prevent the entry of water into the stepping motor main body 20. A motor brush 25 is disposed to retain the motor shaft 24 in a central opening of the motor holder 21. The lower section of the motor shaft 24 is fixed by caulking to the spring holder 26 and a joint 27. 28 is a spring which is disposed between the motor holder 21 and the spring holder 26 and which pushes the motor shaft 24 in a direction opening the valve.
30 are bobbins which are wound coils 31. 32 and 33 are yokes. A magnetic path is formed through the outer periphery of the yokes 32 and 33. 34 are terminals which are electrically connected to coils 31. The terminals 34 and a motor housing 35 form a connector. 36 is a plate which shields the two coil sections magnetically. 37 is a plate preventing resin from flowing into the coil inner section when the motor housing 35 is exterior molded.
40 is a magnet. 41 is a rotor retaining a magnet. The magnet 41 has a threaded section 41a threadably attached to a threaded section 24a of the motor shaft 24 on an inner periphery and an axial stopper 41b of the motor shaft 24. 42 are bearings mounted on both ends of the rotor 41. 43 is a stopper pin press fitted to the motor shaft 24.
This type of stepping motor main body 20 maintains a waterproof structure due to the motor holder 21 fixed to the lower section of the stepping motor main body 20 and is mounted on the top section of the valve housing 1 so that the axial centers are aligned by a mounting screw 44.
The operation will be described below.
Firstly, when the engine is started and the valve is completely closed, the rotor 41 which contains a magnet 40 rotates in a stepwise manner in a direction of valve opening due to a pulsed voltage sent from the control unit (not shown) to the terminals 34 during the valve opening operation. The stepwise rotation is converted into linear motion by the threaded section 41a of the rotor 41 and the threaded section 24a of the motor shaft 24 and the motor shaft 24 displaces in a direction of valve opening (downwardly). As the displacement continues, at the moment when the upper face of the tip 6a of the valve rod 6 near the valve housing 1 abuts with the lower face of the motor shaft 24 near the motor housing 35, the valve rod 6 is depressed by the drive force of the motor shaft 24 against the pushing upward force of the coil spring 11. Also the valve 8 which is mounted on the lower section of the valve rod 6 is lowered and opens with respect to the valve seat 5 and the inlet port 2 and the outlet port 3 are connected by the passage 4.
During the valve closure operation, the rotor 41 which contains a magnet 40 rotates in a stepwise manner in a direction of valve closure due to a pulsed voltage sent from the control unit (not shown) to the terminals 34 in an operation which is the opposite of the above. The motor shaft 24 displaces in a direction of valve closure (upwardly) due to the rotation. In addition to the rotation, the valve rod 6 is raised by the upward pushing force of the coil spring 11 and the valve 8 covers the opening of the valve seat 5.
The waterproofing structure of the stepping motor main body 20 in this type of exhaust gas recirculation valve device is realized by pressing a motor holder 21 by an O-ring 22 onto the lower section of the stepping motor main body 20 and by covering and closing the space between the stepping motor main body 20 and the motor holder 21 with a clamp screw 23 as the O-ring is compressed.
However the unit price of O-rings is relatively high and thus in order to reduce the overall cost of the exhaust gas recirculation valve device, it is required to maintain the waterproofing structure of the stepping motor main body 20 without using an O-ring 22.
The present invention is proposed to solve the above problems and has the object of providing an exhaust gas recirculation valve device which maintains a waterproof structure in the stepping motor main body 20 without using an O-ring 22.
The exhaust gas recirculation valve device according to the present invention is provided with a motor main body which has a motor driving a valve with a valve rod in an opening or a closing direction, and a motor holder which covers the lower opening of the motor main body. One of the lower opening of the motor main body and the upper section of the motor holder is formed a circular groove and the other of the lower opening of the motor main body and the upper section of the motor holder is formed in a protrusion which fits in the circular groove. A liquid sealant is applied between the top of the protrusion and the bottom of the circular groove facing the top of the protrusion. In this way in contrast to the prior art, it is not necessary to use an O-ring which has a relatively high unit price and thus it is possible to reduce the overall manufacturing costs of the exhaust gas recirculation valve device. Furthermore it is possible to ensure maintenance of the waterproofing structure of the motor main body without a threaded stopper since a liquid sealant is used which can be easily adapted to the surface structure of the section to which the sealant is applied.
The present invention is provided with a circular groove which has a bottom and an innermost circular periphery which is adjacent to the bottom and a protrusion which has a top and an innermost circular periphery which is adjacent to the top. The present invention is adapted so that the top of the protrusion and the bottom of the circular groove are placed in contact through the liquid sealant with the innermost periphery of the protrusion fitted to the innermost periphery of the circular groove. Thus excess liquid sealant which is interposed between the bottom of the circular groove and the top of the protrusion is prevented from flowing into the motor main body by a fitted section comprising the circular groove and the protrusion. Therefore it is possible to prevent unexpected defects in motor operation due to the liquid sealant.
Since the present invention fixes a section of the outermost periphery of the circular groove by caulking to the outermost periphery of the protrusion, it is possible to fix the motor holder and the motor main body while keeping the space for leading the excess liquid sealant and thus ensure a waterproofing structure in the motor main body.
Since the present invention is adapted to make a clearance between the outermost periphery of the circular groove and the outermost periphery of the protrusion facing the outermost periphery greater than the clearance between the innermost periphery of a circular groove and the innermost periphery of the protrusion. In this way, it is possible to form a space to store excess liquid sealant between the respective outermost peripheries of the circular groove and the protrusion.
The present invention is adopted to form a hollow to store the excess liquid sealant on the top of the outermost periphery of the protrusion. In such a way, it is possible to effectively store the excess liquid sealant in the hollow.
The present invention is adopted to make a clearance between the bottom of the circular groove and the top of the protrusion facing the bottom of the circular groove greater than the clearance between periphery of the protrusion. In such a way, it is possible to form a space to store the excess liquid sealant between the respective outermost peripheries of the circular groove and the protrusion.
The present invention is adapted to form a hollow to store excess liquid sealant in the bottom of the outermost periphery of the circular groove. In such a way, it is possible to effectively store excess liquid sealant in the hollow.